J. 2005. Overcompensation and adaptive plasticity of apical dominance in Erysimum strictum (Brassicaceae) in response to simulated browsing and resource availability. Á/ Oikos 111: 179 Á/191.In the cases where overcompensation has been observed in monocarpic herbs, overcompensation is associated with an apically dominant shoot architecture of intact plants, increased lateral branching following herbivory, and increased reproductive success as a consequence of damage. The compensatory continuum hypothesis expects overcompensation to be more prevalent in resource rich environments compared to poor environments. This is paradoxical since in resource rich conditions the intact plants should branch most vigorously and hence any further increase in branch number should lead to lower seed yield. An explanation could be that apical dominance is rather insensitive to changes in resource availability, and that overcompensation is possible in conditions where plants experience meristem limitation (due to apical dominance) in relation to available resources.We explored the branching patterns and fitness responses of tall wormseed mustard (Erysimum strictum ) to simulated browsing, soil nutrients, and competition in common garden. Competition increased apical dominance and reduced plant fitness whereas fertilization had the reverse effects. Simulated browsing increased lateral branching and had little impact on plant fitness. Fitness overcompensation was observed only among plants grown in competition and in the absence of fertilization Á/ the most resource poor treatment combination in the experiment. The results contradict both with the compensation continuum and the assumption that apical dominance shows no or very little plasticity in relation to growing conditions. Because directional selection gradients on branch number were invariantly positive irrespective of growing conditions, we propose that, in spite of phenotypic plasticity of apical dominance, the plants appear to be meristem rather than resource limited, and that meristem limitation is strongest in conditions where intact plants produce fewest lateral branches. Our results deviate from the compensation continuum because resource availability affected compensation ability more strongly through phenotypic plasticity of shoot architecture rather than via changes in resource availability per se.

The most sustainable method for treating sewage sludge depends strongly on the situation and local circumstances. In sparsely populated northerly areas are demanding boundary conditions, e.g. cold and long winter, long transport distances and low amounts of generated sludge. In this study, commonly used calculators and emissions coefficients for calculating the greenhouse gas (GHG) emissions from sewage sludge treatment methods were assessed to create a calculator suitable for the Northern Finland context. The calculator was then used to determine which sewage sludge treatment method (composting, anaerobic digestion (AD), incineration (with and without thermal drying)) resulted in the lowest emissions of the GHG gases in different situations in Northern Finland. GHG gases included carbon dioxide (CO2; including biobased), methane (CH4) and nitrous oxide (N2O), measured as carbon dioxide equivalents (CO2eq). According to the calculator, AD generated the least CO2eq emissions of all treatment methods studied. The second best option was incineration of sludge without thermal drying, while the third best was composting or incineration of sludge after thermal drying with e.g. fossil or other fuels. Most of the emissions were generated from the treatment process itself and the share of emissions generated during transport was minimal, despite the long transport distances when all CO2 emissions (incl. biobased) were considered. The role of users of the end-products and the possibility to use the CO2 generated were highly important when considering environmental perspective. These results can be utilized when selecting the locally most suitable method. In future, some of the treatment methods (i.e. AD, incineration) with CO2 capture could be considered carbon sinks, as they also remove biobased CO2 emissions.

Since mycorrhizal symbionts are dependent on host carbon availability, shading and grazing of the host plant often decrease mycorrhizal colonization in host roots. We conducted field experiments on an intensively mycorrhizal host, Autumn gentian, Gentianella amarella to investigate the effects of neighbor removal and simulated grazing on host growth and reproduction as well as mycorrhizal colonization. In the neighbor removal experiment, we manually removed the above-ground parts of companion plants of gentians. Reduced competition tended to improve the performance of both the host and the symbionts. Total fungal as well as arbuscular, hyphal, and coiled hyphal colonizations were higher in gentians with neighbors removed. Simulated grazing (clipping off 50% of shoot height) reduced host shoot and seed biomass, whereas the responses of the root symbionts were most often positive or neutral. In the first experiment (with late-flowering plants), clipping increased arbuscular, hyphal, and total colonizations but decreased dark septate endophyte colonization.In the second experiment (with both early-and late-flowering plants), clipping did not affect total mycorrhizal colonization. Higher arbuscular, hyphal, and total colonizations were found in late-flowering gentians compared to early-flowering ones. Earlyflowering plants, on the other hand, tolerated simulated grazing better compared to late-flowering plants, which may indicate a higher cost of the symbionts for the late-flowering plants. Above-ground herbivory tends to increase carbon limitation, and under these conditions, regrowing shoots and the fungal symbionts may appear as alternative, competing sinks for the host's limited carbon reserves.

Some monocarpic plants show surprising variation in response to natural and simulated grazing. In favourable conditions, injured plants may grow larger and produce more fruits and viable seeds compared with their uninjured counterparts. Such overcompensation, however, is associated with potential costs, particularly delays in flowering and fruit maturation. These delays may further increase a risk of frost injury before seed maturation in the early autumn. We tested the effects of artificially advanced night frosts on the compensatory capacity (i.e., the capacity to compensate the lost biomass by regrowth) of the monocarpic herb Erysimum strictum P. Gaertn., B. Mey., and Scherb. in a common garden experiment. Two simulated herbivory treatments were applied: 25% apical clipping in early vs. late June. Frost treatment was applied in a climate chamber in late August – early September, about 3 weeks before the first natural frost period. Apically damaged plants not exposed to frost treatment produced 1.9–2.6 times more total biomass and 2.5 times more fruit than intact plants. Frost treatment reduced plant performance by 35%–48%, but in contrast to our expectation, there was no significant difference between intact and apically damaged plants in response to early frost. In spite of the delay in phenology, compensatory regrowth did not increase the risk of frost injury. We conclude that while early night frosts imply a potential risk to monocarpic herbs recovering from herbivory, possibly other suboptimal conditions, such as drought in late summer, may provide a greater threat for early-flowering meadow and grassland plants recovering from grazing. Possibly multiple selective forces and environmental risk factors operate together in the evolution of grazing tolerance associated with flowering phenology, plant growth strategy, and architecture.

In biennial plants, the age of flowering is constrained, but size at flowering is highly variable. This suggests that performance at the flowering stage depends largely on growth conditions at the rosette stage. We examined this possibility using Erysimum strictum P. Gaertn., B. Mey., and Scherb. (Brassicaceae), a strictly biennial herb, the reproductive output of which increases with increasing plant height and branch number. In a common garden experiment, we defoliated (50% of leaves removed twice) and fertilized (three times) individual plants at the rosette stage and studied their performance at the flowering stage in the following year. Rosette defoliation adversely affected all performance measures except seed number per fruit and seed weight. Fertilization did not alleviate these effects. Defoliation reduced seed set by 48% in fertilized plants and 29% in unfertilized plants. Fertilization stimulated branch production from the rosette base but did not significantly affect plant height. These observations suggest that, in the case of basally unbranched plants, apical dominance by the leading stalk suppresses the axillary meristems at the rosette base. Fertilization at the rosette stage can break this suppression. The induction for breakage presumably occurs before bolting since, in our earlier experiments, neither fertilization nor apical damage at the flowering stage stimulated branching from the base. Erysimum strictum is likely to be selected for fast vertical growth at the start of bolting, and hence plant height is a less plastic trait with respect to resource availability than branch number. Regression analysis suggested that, in response to rosette fertilization, small plants invest in height growth instead of branching, whereas large plants to a greater extent invest their supplemental resources in vigorous branching. Consequently, resource availability at the rosette stage influences apical dominance at the flowering stage. Unexpectedly, however, improved resource availability did not alleviate the cost of simulated rosette-stage herbivory.Key words: apical dominance, biennial, fitness, herbivory, resource availability, rosette stage.